In recent years, a digital coherent optical transmission technique has been put into practice, and a high-reliable long-distance large-capacity transmission accommodating various ultra high-speed client signals in an ultra high-speed single wavelength channel having a speed equal to or more than 100 Gbit/s has been realized.
A block configuration diagram of a generally-available digital coherent optical transmission/reception device is shown in FIG. 11. The generally-available digital coherent optical transmission/reception device is implemented with an optical transmission light source 10000 and an optical reception light source 20000. A control unit 50000 respectively adjusts the optical output powers of the optical transmission light source 10000 and the optical reception light source 20000, thus optimizing the transmission and reception property.
The light which is output from the optical transmission function light source 10000 is optically modulated by the optical modulation device 30000, and is output as an output signal light. The light which is output from the optical reception light source 20000 interferes with an optical signal which is input into the optical reception device 40000 as a local oscillation (LO: Local Oscillator) light.
In this case, the wavelength of the light which is output from the optical reception light source 20000 interferes with the optical signal which is input into the optical reception device 40000, and therefore, the wavelength needs to be the same as the wavelength of the input optical signal. The digital coherent optical transmission/reception device uses a wavelength variable light source as the light source at the reception side, thereby changing the wavelength of the LO light in accordance with the wavelength of the input optical signal. Therefore, in a case where a wavelength division multiplexing (WDM: Wavelength Division Multiplexing) optical signal is input, a particular wavelength can be selectively received from the WDM signal.
On the other hand, in the digital coherent optical transmission/reception device, the demand for reducing electric power consumption and reducing the size is increasing. As a technique for reducing electric power consumption and reducing the size of the digital coherent optical transmission/reception device, for example, a technique has been suggested to make the optical transmission function light source and the optical reception function light source into a common light source, and reduce the light source implemented on the digital coherent optical transmission/reception device.
PTL 1 discloses an optical communication transmission/reception device in which an optical switch switches an output light from a light source into an optical transmission circuit or an optical reception circuit, and in which an optical split circuit splits the output light from the light source into an optical transmission circuit and an optical reception circuit, although this is not a digital coherent optical transmission/reception device.